460 Take Home Exam

0. Demo of LAST assignment sh (and any other missing Labs):

   sign up with the TA to demo in his office on/before Thur, 4-24-08
   Sign up for oral with KCW in sloan 321 on Friday 4-25-08

             DUE: 6 PM, Monday April 28, 2008
                  (TextEdit and Printed copy)
 
1. Assume: 1.44 MB floppy disk contains a bootable MTX image, whose disk 
   block numbers are stored as a sequence of ushort numbers in the last block 
   (block 1439) of the disk. The sequence of numbers ends with a 0. As usual, 
   block 0 contains a MTX booter.

   DO: Write pseudo-C code for such a MTX booter. 
  (BONUS): Create and Demo such a bootable FD on Monday, 4-28-08


2. Assume: The tswitch() function in our MTX kernel is modified as
              .globl  _tswitch, _scheduler, _running, _int100h
     _tswitch:
                 int  100
                 ret      
     _int100h: !--------------------------------- 
               !  Interrupt handler for INT 100
               !---------------------------------
                
     DO: Write assembly code for the INT 100 Interrupt handler shown in the 
         dashed box. 
     (BONUS): Demo YOUR MTX (based on Lab#5.2) with the modified tswitch().
 
3. The exec syscall in the MTX system of the SH assignment has the form
            int r = exec(cmdLine) char *cmdLine
   where the string cmdLine is passed to the target program as
               main(s) char *s;

   DO: Use pseudo-C code and diagrams (plus words) to explain HOW IS THIS DONE?
  (Start from the current Umode image that issues an exec("mkdir /a/b/c");
   When the task executes kexec() in the MTX kernel: what does it do so that
   the string "mkdir /a/b/c" will be accessable as main(s) in the new image?)

4. Given : A semaphore s, with s.value = 2 and s.queue = 0 initially.
           A sequence of P, V operations on s as shown below:
  ===============================================================
        time:   0   1    2    3    4    5    6    7    8
              -------------------------------------------
     TaskID :       1    2    2    3    4    1    2    3
   Operation:   -   P    P    V    P    P    P    V    V
  ===============================================================

DO: Show the semaphore value and queue contents between the time instants.
    s.value  :
    s.queue  :

5.  Refer to the serial driver in LAB #8.
    (a). The shown code supports only ONE serial terminal at 0x3F8.
         Explain HOW TO support an ADDITIONAL serial terminal at 0x2F8.

    (b). When a task calls sputline(), it only puts a line of chars into the
         output buffer, outbuf[].
         Explain: How are the chars actually sent out?

    (c). What's wrong with the following do_tx() code? WHY?

         struct semaphore outdata; // outdata.value = # of chars in outbuf[ ]  
         struct semaphore outroom; // outroom.value = # of rooms in outbuf[ ] 
 
         int do_tx()
         {
             P(&outdata);    // wait if no data in outbuf[ ]
              output a char from outbuf[ ]
             V(&outroom);    
         }